Osmosis Flashcards
What is osmosis?
a type of diffusion of water across a partially permeable membrane
water molecules move between solutions but solutes usually cannot
there will be a net movement of water from the solution with a higher water potential to the solution with a lower water potential
this will continue till the water potential is equal
What is water potential?
the pressure exerted by water molecules as they collide with a membrane or container
it is measured in units of pressure (Pa), the symbol for water potential is Ψ
What is the highest value for water potential?
What causes water potential to lower?
pure water has a water potential of 0kPa (at room temp and atmospheric pressure)
the presence of solutes in water lowers the water potential below zero
the more concentrated a solution is the more negative the water potential
What is hydrostatic pressure
when water diffuses into a closed system such as a cell it increases the hydrostatic pressure inside the cell because the volume of water increases inside the cell
measured in kPa
What is the effect of high hydrostatic pressure?
if an animal cell is placed in a solution with a higher water potential than that of the cytoplasm water will move into the cell by osmosis, increasing the hydrostatic pressure
animal cells have no cell wall and the membrane cannot stretch much, eventually the membrane will break and the cell will burst
when the cell bursts it is called cytolysis
What happens if the cell is placed in a solution with a lower water potential?
reduction in volume of the cell
referred to as crenation
How do cells prevent cytolysis or crenation?
multicellular animals usually have control mechanisms to make sure their cells are continuously surrounded by aqueous solutions with an equal water potential (isotonic)
in blood the aqueous solution is plasma
What happens to plant cells in solutions with different water potential?
cellulose cell walls prevent bursting
the hydrostatic pressure pushes the membrane against the wall, this is called turgor
the cell is said to be turgid
when the water potential is lower the cell surface membrane moves away from the cell
the cell is said to be plasmolysed
